Recently, active research has been conducted on a method of efficiently utilizing a radio frequency (RF), which is a limited resource, in a mobile communication system. In wireless communication, an error occurs in transmitted information due to thermal noise of a receiver and/or frequency selective fading, and frequency utilization efficiency is degraded by the error. As an error-correcting method of correcting the error due to the thermal noise in a receiver, a convolutional code such as a non-systematic convolutional (NSC) code or a recursive systematic convolutional (RSC) code, a low density parity check (LDPC) code, a turbo code, which is a parallel concatenation of RSC codes, and the like are used (see Non-Patent Document 1). In particular, encoders for generating RSC codes, which are component encoders (RSC encoders), are concatenated in parallel via an interleaver to perform turbo encoding in an encoding section of a transmitter when the turbo code is used. On the other hand, it is possible to achieve characteristics close to a Shannon limit by performing turbo decoding in which an iterative decoding process is performed in a decoding section of the receiver. Here, the turbo code is used in an encoding scheme for independently performing encoding in each RSC encoder by providing a plurality of RSC encoders in an encoder and applying an interleaver to information bits to be encoded.
As a technique of compensating for frequency selective fading, a technique of a frequency-domain equalization process is generally used. For example, there is a technique based on a minimum mean square error (MMSE) criteria or the like.
Further, the improvement of reception characteristics by turbo equalization technology (see Non-Patent Document 2) in which an iterative decoding technique used for a turbo code is applied to an equalizer and a decoding section has also been studied. In general, it is possible to eliminate the effect of inter symbol interference (ISI) as much as possible by iterating an inner code and an outer code as which the convolution of transmission signals and impulse responses, and constraint of information bits by error correcting encoding are respectively regarded in single carrier transmission. In addition, the use of a turbo code which is capable of obtaining good reception characteristics is being studied as an error-correcting code for use in turbo equalization (see Patent Document 1). Here, the turbo equalization is a technique of detecting a signal by exchanging external information by iterative processes of a maximum a posteriori (MAP) detector and a decoder based on the turbo principle. A MAP detector for a single carrier is a soft canceller that cancels a replica of ISI fed back from the decoder, inter-user interference, inter-cell interference, inter-antenna interference, or the like, and is used for frequency-domain equalization. The MAP detector is also applicable to multi-carrier. In this case, the MAP detector becomes a soft canceller that cancels a replica of inter-code interference, inter-carrier interference, or the like.
On the other hand, there is multiple-input multiple-output (MIMO) transmission of multi-antenna technology as transmission technology that improves frequency utilization efficiency.
In addition, there is technology in which a spectrum, which is an applicable frequency-spread signal, is allowed to be allocated to a partially overlapping frequency range when the number of reception antennas of a receiver is less than the number of transmission antennas, and the receiver detects a signal by turbo equalization, which is iterative equalization technology (see Patent Document 2).